Recently on a oneworld itinerary connecting through Düsseldorf Airport (DUS), I was able to visit the Hugo Junkers Lounge, which is contracted by several airlines to serve their premium passengers. As I said in my review of the Hamburg Airport Lounge, I’m always iffy when it comes to third-party lounges, so I headed up the elevator with cautious optimism.
As a oneworld Sapphire elite member (in my case, Platinum on American Airlines), flying with Oneworld partners grants me access to airport lounges, though with the caveat that lounges operated by third parties may not be available. Fortunately, that restriction wasn’t in place on this trip; previously, flying Air Berlin on my first leg from Hamburg (HAM) to DUS, I was given access to the Hamburg Airport Lounge. My next leg from DUS to London Heathrow (LHR) was on British Airways, which contracts with the Hugo Junkers Lounge operated by DUS, to which I was also granted access thanks to my status.
Wikipedia: Who is Hugo Junkers?
The Hugo Junkers Lounge also contracts with several other airlines departing out of in the Schengen zone (read: mainly any airline not named Lufthansa), as well as a few membership programs. One could also pay €21 for access (credit cards only).